Git checkout does not change anything

Question

I really like git. At least, I like the idea of git. Being able to checkout my master project as a separate branch where I can change whatever I want without risk of screw

Answer 1

$ git branch
* master
$ git checkout -b develop
$ git branch
  master
* branch

Now change whatever you want and do git add .

$ git add .   <--Here is the source of the problem, always git add . at your branch to see the observable difference between two branches.
$ git commit -m "Some messages"

$ git checkout master
$ git branch
*master
develop

Everything is neat and clean.